[BB_TX]

A little different, but here is what I did installing a 5th Airborne on box. Alone.

Backed truck so tailgate was under pin box.
Lowered trailer until old pin box was just barely above tailgate.
Removed bolts and let pin box ease down on tailgate.
Raised trailer until frame cleared old pin box and moved it to the side.
Moved new pin box under frame.
Lowered trailer until frame dropped over new pin box and holes were close.
Used large screwdriver to align holes and inserted bolts.

You could probably do something similar by using some blocks to hold up the Goosebox when installing it. Or maybe a friend to help hold it up.